acts like the germinal center of the lymph node for T-cells. There is a lot of selection for T cells in the Thymus that properly rearrange receptors. Unlike B cells which finish rearrangement in the marrow, T cells complete their rearrangement in the Thymus then are selected on the thymic epithelium based on whether they have auto Ag or allo Ag. Then they emigrate to the periphery just like B cells